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HyperClone Feature Guide for File

OceanStor Dorado V3 Series V300R002

This document is applicable to OceanStor Dorado5000 V3, Dorado6000 V3, and Dorado18000 V3. It describes the implementation principles and application scenarios of the HyperClone feature (for file), and explains how to configure and manage HyperClone.
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Working Principle

Working Principle

This section describes the working principle of HyperClone for file.

Related Concepts

  • Redirect-On-Write (ROW)

    ROW is the core technology of snapshot. After receiving a write request, the storage system writes new data to a new storage location and directs the pointer of the modified data block to the new location. Old data serves as the snapshot data.

  • Parent file system

    A file system functioning as the data source is called as a parent file system. A clone file system can also be used as a parent file system.

  • Child file system

    A file system cloned from a parent file system is called a child file system.

  • Cascading clone

    Creating a clone file system based on another clone file system is called cascading clone.

  • Splitting

    A clone file system can be split from its parent file system and become an independent and complete file system.

Read/Write Principle of a Clone File System

A clone file system is a readable and writable copy at a point in time based on the ROW and snapshot technologies.

A clone file system can be created using a new snapshot or an existing snapshot. If using a new snapshot, the storage system will automatically generate a snapshot at the point in time when the clone file system is created. Alternatively, existing common snapshots, periodic snapshots, and HyperReplication/NAS HyperMetro/HyperVault private snapshots can be used for clone.

Before data of a clone file system is modified, the clone file system shares source data with the parent file system. The snapshot is used to ensure data consistency at the point in time when clone is performed, as shown in Figure 1-1. The clone file system is shared for application servers to read and write. At this moment, the read data is the source data in the parent file system.

Figure 1-1 Status of data in the clone file system before data is changed

When an application server tries to write new data to an existing data block in the parent or clone file system, the storage system allocates new storage space for the new data and so the original data will not be overwritten. As shown in Figure 1-2, when the application server tries to modify data block A of the parent file system, the storage pool allocates new data block A1 to store new data, and data block A is not released; when the application server tries to modify data block D of the clone file system, the storage pool allocates new data block D1 to store new data, and data block D is not released. Data in the file system snapshot is not changed during this process.

Figure 1-2 Status of data in the clone file system after data is changed

Working Principle of Splitting

The storage system allocates new data blocks to store the shared source data separately and retains data newly written to the clone file system, and then cancels the relationship between the clone file system and the snapshot of the parent file system. After being split from the parent file system, the clone file system becomes an independent and complete physical data duplicate. Figure 1-3 shows the process.

Figure 1-3 Process of splitting a clone file system from its parent file system
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Updated: 2019-02-22

Document ID: EDOC1100067321

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